Rocket motor



O. C. WILSON ROCKET MOTOR July 13, 1954 Filed Aug. 13, 1945 Il l I! wir#,lil In AIIM ATTORNEY Patented July 13, 1954 ROCKET MOTOR Olin C.Wilson, Pasadena, Calif., assignor to the United States of America asrepresented by the Secretary of the Navy Application August 13, 1945,Serial No. 610,652

1 Claim.

This invention relates to rocket missiles, such as rocket projectiles,rocket bombs and the like, and has particular relation to rocket motorsfor use therewith.

Conventional rocket motors used for jet propelling projectiles, bombsand the like generally comprise a cylindrical motor tube containing apropellent charge, an igniter for initiating combustion of thepropellent and exhaust nozzle means mounted at the rear end of the motortube for releasing the products of combustion under pressure, therebypropelling the rocket in a direction opposite to the flow of exhaustgases. Rocket motors of this type have the disadvantage that thequantity and size of the propellent charge is limited by the effectivethroat area of the exhaust nozzle means.

In the construction of high performance rocket motors employingpropellent grains, as the propellent grain is increased in volume, thenozzle diameter may be increased so as to give a constant ratio ofburning area of the propellent grain to throat area of the nozzle.However, the value of the ratio of burning grain area to thecross-sectional internal port area within the motor tube increasessteadily with increase in grain length and experiments have shown thatrocket motors are unsuccessful if the latter ratio is greater thanapproximately '75% of the former ratio. rJhe cross-sectional internalport area is defined as the radial cross-sectional area within the motortube not occupied by the propellent grain. One cause of failure of highperformance rocket motors is the formation of excessve pressure withinthe motor tube caused by decreases in the cross-sectional internal portarea within the motor tube due to cross-sectional area increases in thegrain. When a rocket is fired, the force of setback acting on thepropellent grain causes it to be compressed along its length, therebyincreasing the cross-sectional area, particularly along the rear endportion of the grain. Another cause of failure is excessive heating ofthe motor tube due to the generation of peak pressures of hot gaseswhich cannot be immediately vented through the exhaust nozzle. By use ofthe present invention, the abovementioned difliculties may be obviated.

In accordance with the present invention there is provided a rocketmotor of novel construction which comprises a motor tube havingrearwardly directed exhaust means mounted forward of the rear endportion of the motor tube, including passage means communicating withthe motor tube. The rearwardly directed exhaust means may be mountedalong the length of the motor tube and is preferably mounted at theforward end portion of the motor tube. The rearwardly directed exhaustmeans of the present invention may be used as the sole exhaust means, orit may be used in combination with conventional rear end portion exhaustnozzles, or a plurality of rearwardly directed exhaust means of thepresent invention may be employed along the length of the motor tube.

An object of the present invention is to provide a rocket motor whichwill permit the use of a longer and increased volume of propellentcharge than has heretofore been possible for a given size of rocketmotor, and which will minimize the possibility of deterioration or otherdamage to the propellent charge due to the rapid acceleration ofburning, and the attendant possibility of erratic burning.

Another object of the invention is to provide a rocket motor which willpermit the discharge of a greater volume of gas from the motor tubewithout exceeding the allowable maximum velocity of burning gases thanhas heretofore been possible.

Another object is to provide a rocket motor which will have a lowinternal gas velocity thereby decreasing the effective heat transferfrom the hot exhaust gases to the motor tube.

Another object is to provide a rocket motor which will permit ashortened travel of combus tion gases Within the motor tube therebydecreasing the friction loss due to the travel of gas within the tube. Y

Another object is to provide a rocket motor which has particular usewith high velocity, long range rocket devices which will maintain apredetermined trajectory due to the reduced burning time of a given sizepropellent grain.

Another object is to provide a rocket device having a decreaseddispersion due to all or part of the thrust being applied at the centerof gravity of the rocket missile.

Another object is to provide a rocket device having rearwardly directedexhaust means mounted at and communicating with the forward end portionof the rocket motor located at the center of gravity of the rocketdevice, whereby to improve the flight characteristics thereof.

Another object is to provide a rocket motor having helically disposed,rearwardly directed exhaust means mounted forward of the rear endportion of the motor tube, preferably at the ceni portion ii `mounted onthe rear end portion i?.

" to protect the nozzl ter of gravity of the rocket device, whereby toimprove the flight characteristics of the rocket.

These and other objects oi the invention will be better understood byreference to the accompanying description and drawing in which:

Fig. l is a longitudinal sectional View oi a high speed, long rangerocket incorporating the present invention;

Fig. 2 is an elevational view of a barrage or bomb driving rocket withthe rearwardly directed exhaust means of the present invention shownpartly in cross-section; and

Fig. 3 is a perspective View of the forward, rearwardly directed exhaustmeans shown in Fig. l.

Referring to the drawing, the rocket device shown in Fig. l. comprises amotor tube It having a forward exhaust end portion l! and a rear exhaustend portion I2. A forward exhaust nozzle unit is mounted on the forwardend and a rear exhaust nozzle unit ifi is A. base is secured to the rearend portion I2 IG and the contents of the motor tube lil during plate IE vRadial hns are secured to the outer rear end portion of the motortube in order to impart stability to the rocket during its iiight.

The interior of the motor tube is divided into a forward compartment l'Iand a rear compartment I8 by an internal center flange Il. A

lcylindrical propellent grain 2t is mounted in the rear compartment bymeans or" a rear spacer grid 2l and a rear center spacer grid 22. Theforward propellent grain 23 is positioned in the forward compartment I'Iby means oi a forward spacer grid 2t and a 'forward center spacer grid25. An igniter 2e mounted on the grid 22 is connected to a source ofelectricalA current (not v shown) by means of ignition wires 2'?.

The rearwardly directed nozzle unit I3 is provided with an externallyscrew threaded socket 3G which is adapted to be screwed into the forwardend portion il of the motor tube. The interior of the nozzle unit I3 hasa socket chamber 3i leading into radial exhaust passages 32communicating with the rearwardly directed nozzlesSf-l. The unit I3terminates at its forward end in a projectile shaped nose 3ft having aninternal cavity 3b'. Iused as an exhaust gas chamber or it may beseparated from the radial exhaust passages 32 -by a suitable steel plugand lled with an ex- `ofthe passages 32 and the nozzles 33 are con- 1plosive and a fuze (not shown). The outer ends tained in the bosses 36.

'in operation, the propellent grains 2E and 23 are ignitedsimultaneously by means of the igniter 26 which is Aelectrically nredyby the passage of current through the ignition wires El.

.pellent grains burn along their surfaces, desig- The flash from theigniter ignites the propellent in the rear compartment IS and passesthrough the opening in flange i9 igniting the propellent 23 in theforward compartment Il. The pro- .nated portions of which may beinhibited from burning by inhibitor means such as described inco-pending application serial No. 618,764 led on September 26, i945. Theburning gases, which generate temperature and pressure of high order, .f

pass along the rear compartment i8 toward the rear exhaust nozzle i4 andpass along the forward compartment il toward the forward nozzle unit I3.The free area through which the gases passalong the length of the motortube is known l handling and shipment The cavity may be.

iuze (not shown) as the internal port area, which is the crosssectionalarea within the motor tube not occupied by the propellent charge. Itwill be apparent that as the surface of the propellent grain burns away,the internal port area is increased, thus permitting the flo-w of agreater volume of gas at a lower velocity. After passing rearwardlythrough the yrear compartment and forwardly through the forwardcompartment, the gases are discharged through the throat of the rearnozzle I4, the base plate I being removed before iiring of the rocket,and forwardly through the socket chamber 3i, radially through theexhaust passages and rearwardly through the throat of `the nozzles 33.

Due to the new of gases within the motor tube,

the pressure is highest'at the center of the motor tube and lowest atthe forward and rear extremities thereof. Therefore it will be apparentthat the pressure diierence between the center and the extremities ofthe motor tube is virtually only hahe of the pressure differential thatwould exist if the same total length of propellent were used and theresultant gases were discharged from the nozzle only. Furthermore, sinceboth the forward propellent charge and the rear propellent chargeignited simultaneously the burning time of rocket motor is substantiallyone-hah" oi that which would be required ii only one grain and oneigniter positioned at one end thereof were provided. The rocketprojectile shown in l may be spin-stabilized; that is, it may be causedto rotate about its longitudinal axis during flight, by spirallydirecting or canting the nozzles Spinning of the rocket may also beaccomplished by providing the rear exhaust end I2 with a canted exhaustnozzle arrangement, suoh as isv shown in co-pending application, Ser.No. 554,337 filed, November 20, lf-lil. in the event that aspin-stabilized rocket projectile is desired, the fins IE may beomitted.

As shown in Fig. 2, the present invention is also vadapted for use in arocket bomb or barrage rocket. rEhe rocket bomb comprises a motor tube iIii having a forward end portion i i i and` a rear yend portion II2 inwhich is mounted a convenever, in place oi the nose 3ft shown in Fig. l,

screw thread means is provided for attachment to a bomb case IE6. Inthis manner the nozzle unit H3 provides an adapter body for connectingthe motor tube I Iii to the bomb case i. The nose of the bomb case isprovided with a sleeve 52 for protecting the arming propeller of a noseThe rocket device is preferably constructed so that the rearwardlydirected exhaust unit H3 is at the center of gravity of the rocketdevice. in this connection it has been found that the positioning of theexhaust means at the center of gravity of the rocket missile greatlyimproves the stability thereof during ight. t will beunderstood thatwhen a rear exhaust unit is mounted in the rear end portion l i2, only aportion of the thrust is applied at the center of gravity by therearwardly directed nozzle unit H3, but even this amount has anappreciable effect' on increasing .the stability and decreasing thedispersion characteristics of the rocket. The propellent charge (notshown) within the motor tube H0 may be of the design shown in Fig. l, orit may comprise a single propellent grain, or the internal arrangementmay be of any suitable construction.

It will be understood that the rearwardly directed nozzle means I3 and||3 of the present invention may be mounted at the forward end of themotor tube, at the center of gravity of the rocket device, or at anydesired position along the length of the motor tube. Although in thedrawing only one forward rearwardly directed nozzle unit is shown, itwill be understood that a plurality of nozzle units may be employedalong the length of the motor tube. Thus, the rocket projectile shown inFig. 1 may be provided with a rearwardly directed nozzle unit betweenthe forward compartment I'I and the rear compartment I8. While it ispreferred to employ exhaust means at the rear end portion of the motortube, it has been found that a rocket device employing the presentinvention will perform satisfactorily Without the use of the rear endportion exhaust means.

I claim:

A rocket motor comprising a motor tube, a rear exhaust nozzle assemblysecured in one end of said tube, a forward exhaust nozzle assemblysecured in the other end of said tube and having exhaust passagesextending radially from and in communication with the interior of saidmotor tube, said exhaust passages terminating in rearwardly directednozzles, an annular flange member secured to the interior of said motortube intermediate the length thereof, a forward pair of propellent grainspacers engaging respectively the inner end of said forward nozzleassembly and the forward end of said anular flange, an after pair ofpropellent grain spacers engaging respectively the inner end of saidafter nozzle assembly and the after end of said annular flange, apropellent grain xedly disposed between each of said forward and afterpairs of grain spacers, and an igniter mounted on one of saidannular-flange-engaging grain spacers, the interior of said motor tubeon one side of said annular ange being in communication with theinterior of the motor tube on the other side of said annular flangewhereby firing of said igniter will cause simultaneous ignition of bothof said propellent grains.

References Cited in the le of this patent UNITED STATES PATENTS NumberName Date 2,206,809 Denoix July 2, 1940 v2,398,927 Farr Apr. 23, 19462,404,190 Pope July 16, 1946 FOREIGN PATENTS Number Country Date 11,705France Oct. 5, 1844 1,734 Great Britain Apr. 24, 1876 503,006 FranceMar. 6, 1920 503,166 France Mar. 10, 1920 139,856 Great Britain Mar. 18,1920 166,583 Great Britain July 11, 1921 618,668 Germany Sept. 13, 1935831,496 France June 7, 1938

